1. Field of the Invention
This invention relates generally to a semiconductor technique and more particularly to a silicone polymer insulation film on a semiconductor substrate and a method for forming the film by using a plasma CVD (chemical vapor deposition) apparatus.
2. Description of Related Art
Because of the recent rise in requirements for the large-scale integration of semiconductor devices, a multi-layered wiring technique has attracted a great deal of attention. In these multi-layered structures, however, capacitance among individual wires hinders high speed operations. In order to reduce the capacitance it is necessary to reduce the dielectric constant (relative premillivity) of the insulation film. Thus, various materials having a relatively low dielectric constant have been developed for insulation films.
Conventional silicon oxide films SiOx are produced by a method in which oxygen O2 or nitrogen oxide N2O is added as an oxidizing agent to a silicon material gas such as SiH4 or Si(OC2H5)4 and then processed by heat or plasma energy. Its dielectric constant is about 4.0.
Alternatively, a fluorinated amorphous carbon film has been produced from CxFyHz as a material gas by a plasma CVD method. Its dielectric constant xcex5 is as low as 2.0-2.4.
Another method of reducing the dielectric constant of insulation film is to use the good stability of Sixe2x80x94O bond. A silicon-containing organic film is produced from a material gas (i.e., a source gas) under low pressure (1 Torr) by the plasma CVD method. The material gas is made from P-TMOS (phenyl trimethoxysilane, formula 1), which is a compound of benzene and silicon. The dielectric constant xcex5 of this film is as low as 3.1. 
A further method uses a porous structure made in the film. An insulation film is produced from an inorganic SOG material by a spin-coat method. The dielectric constant ∈of the film is as low as 2.3.
However, the above noted approaches have various disadvantages as described below.
First, the fluorinated amorphous carbon film has lower thermal stability (370xc2x0 C.), poor adhesion with silicon-containing materials and also lower mechanical strength. The lower thermal stability leads to damage under high temperatures such as over 400xc2x0 C. Poor adhesion may cause the film to peel off easily. Further, the lower mechanical strength can jeopardize wiring materials.
Oligomers that are polymerized using P-TMOS molecules do not form a linear structure in the vapor phase, such as a siloxane structure, because the P-TMOS molecule has three Oxe2x80x94CH3 bonds. The oligomers having no linear structure cannot form a porous structure on a Si substrate, i.e., the density of the deposited film cannot be reduced. As a result, the dielectric constant of the film cannot be reduced to a desired degree.
Further, the SOG insulation film of the spin-coat method has a problem in that the material cannot be applied onto the silicon substrate evenly and another problem in which a curing system after the coating process is costly.
Objects of the Invention
It is, therefore, a principal object of this invention to provide an improved insulation film and a method for forming it.
It is another object of this invention to provide an insulation film that has a low dielectric constant, high thermal stability, high humidity-resistance and high O2 plasma resistance, and a method for forming it.
It is a further object of this invention to provide a material for forming an insulation film that has a low dielectric constant, high thermal stability, high humidity-resistance and high O2 plasma resistance.
It is a still further object of this invention to provide a method for easily forming an insulation film that has a low dielectric constant without requiring an expensive device.
One aspect of this invention involves a method for forming an insulation film on a semiconductor substrate by using a plasma CVD apparatus including a reaction chamber, which method comprises a step of introducing a silicon-containing hydrocarbon compound expressed by the general formula Sixcex1Oxcex2CxHy (xcex1, xcex2, x, and y are integers) and then introducing it to the reaction chamber of the plasma CVD apparatus, and a step of forming an insulation film on a semiconductor substrate by plasma polymerization reaction. A reduction of the total flow of the reaction gas is one of the features of the present invention. The residence time of the reaction gas including the material gas (i.e., the source gas) can be lengthened by, for example, reducing the total flow of the reaction gas. In an embodiment, an additive gas can be introduced to further control the flow of the reaction gas and to adjust plasma polymerization reaction, although the additive gas can be eliminated entirely. According to the present invention, a silicone polymer film having a micro-porous structure with a low dielectric constant can be produced. In the above, plasma CVD includes LCVD excited by microwaves. In addition, the vaporization method adapted to the present invention includes a direct vaporization method, a baking method, and a bubbling method which will be explained later.
In an preferable embodiment, the silicon-containing hydrocarbon compound is a compound of the formula, Sixcex1Oxcex1xe2x88x921(R)2xcex1xe2x88x92xcex2+2(OCnH2n+1)xcex2 (R is C1-6 hydrocarbon, xcex1, xcex2, x, and y are integers), and in another preferable embodiment, the R is CH3.
The present invention is also drawn to an insulation film formed on a semiconductor substrate, and a material for forming the insulation film, residing in the features described above.